A complete active space self-consistent field multiconfiguration referenceconfiguration interaction study of the potential energy curves of the ground and excited states of CCl

The potential energy curves have been examined for the ground (X (2)Pi) and excited states (1 (2)Delta, 1 (2)Sigma (+), 2 (2)Sigma (+), and 1 Sigma (- )) of CCl using complete active space SCF (CASSCF) and multiconfiguration r eference internally contracted configuration interaction (MRCI) with the au g-cc-pVTZ basis set. The active spaces are comprised of all valence molecul ar orbitals and include some nonvalence virtual molecular orbitals, which a re used to further confirm the nature of the excited states. The anharmonic vibrational energy levels are also obtained for the ground and excited sta tes based on the potential energy curves calculated with different active s paces. A comparison with experimental results is made and discussed. (C) 20 01 American Institute of Physics.